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L-Rhamnose Dehydrogenase LraA of Aspergillus niger Shows High Substrate Specificity Matching Its Expression Profile

Summary

Scientists studied an enzyme called LraA found in a common fungus (Aspergillus niger) that breaks down L-rhamnose, a sugar found in plant cell walls. They discovered that this enzyme is extremely selective and only works on L-rhamnose, unlike most other similar enzymes that can process multiple types of sugars. This makes it very useful for biotechnology applications where researchers want to specifically convert L-rhamnose without affecting other pathways.

Background

L-rhamnose is a major monomeric sugar component of pectin polysaccharides found in plant cell walls. Aspergillus niger metabolizes L-rhamnose through a non-phosphorylated pathway, with the first step catalyzed by L-rhamnose dehydrogenase (LraA), which converts L-rhamnose to L-rhamnono-γ-lactone.

Objective

To heterologously produce and biochemically characterize A. niger LraA enzyme and study its expression patterns on various monosaccharides to determine substrate specificity and functional role in fungal sugar catabolism.

Results

LraA demonstrated high specificity for L-rhamnose with activity of 63.4 U·mg⁻¹, with only 1.15 U·mg⁻¹ activity on L-fucose and no activity on other substrates tested. Gene expression analysis showed lraA was specifically expressed on L-rhamnose, matching its narrow biochemical specificity and NAD⁺ cofactor dependency.

Conclusion

LraA evolved with highly specific function in L-rhamnose catabolism, unlike most other sugar reductases/dehydrogenases. This specificity benefits L-rhamnose-based biotechnological applications but limits use in multi-sugar conversion processes.
  • Published in:Journal of Fungi,
  • Study Type:Experimental Research,
  • Source: 40278122
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